1. Field of the Invention
The present invention relates to a touch display, and more particularly to a display panel having a touch function, a display device and a control method for the same.
2. Description of Related Art
A touch screen is also known as a touch panel. The touch screen is a liquid crystal display device which can receive an input signal of a touch event such as a finger contact. When a user touch a graphic button on the screen, a touch feedback system can determine a touch position according to a preset driving and scanning method such that the touched graphic button is determined and an instruction type is also determined. Comparing to the conventional mechanical button panel, the touch screen is more convenient, so that the touch screen has been widely used.
A projected capacitive touch screen is one of common touch screens. The projected capacitive touch screen utilizes a touch technology of a capacitance change generated by a finger to approach the capacitive touch screen. The touch technology can be divided into a self-capacitance type and a mutual-capacitance type. The touch technology can also be divided into an out-cell type and an embedded type. The embedded type can also be divided into an in-cell type and an on-cell type. Using the in-cell and self-capacitance touch technology as an example, multiple touch electrodes are formed on a surface of a glass substrate and are made of a conductive material. The touch electrodes are respectively connected with a controller through lead wires. The touch electrodes respectively formed capacitors with a ground, which is called the self-capacitance. When a finger touch a touch screen, the capacitance of the finger will add on a screen capacitor such that the quantity of electric charge of the screen capacitor is increased. According to a capacitance change before and after touching by the finger, a touch position is determined.
With the development of the touch screen technology, the in-cell technology is gradually become the mainstream technology for medium and small size touch screen. Through integrating the touch electrodes into a cell of a panel, and through the same controller IC to process a display signal and a touch screen signal respectively by a time-division multiplex control method such that the thickness and the weight of the touch display panel are reduced.
As shown in FIG. 1, FIG. 1 is an equivalent circuit diagram of a touch display panel according to the conventional art.
The display panel includes a data line 101 and a scanning line 102, a signal control line 103, a first thin-film transistor (TFT) T1, a second thin-film transistor (TFT) T2, a liquid crystal capacitor CLC and a storage capacitor Cst1. A gate of the first TFT T1 is connected with the scanning line 102. A source of the first TFT T1 is connected with the data line 101. A drain of the first TFT T1 is connected with terminals of the liquid crystal capacitor CLC and the storage capacitor Cst1 which are connected in parallel. Another terminal of each of the liquid crystal capacitor CLC and the storage capacitor Cst1 is connected with a drain of the second TFT T2. A source of the second TFT T2 is connected with the signal control line 103. A gate of the second TFT T2 is connected with a common electrode 104. When the signal control line 103 controls the T2 to be turned on, the touch display panel is in a display mode. Through the data line 101 and the scanning line 102 the liquid crystal capacitor CLC and the storage capacitor Cst1 are charged and discharged in order to control the deflection of the liquid crystal molecules so as to realize a different display screen. When the signal control line 103 control the second TFT T2 to be turned off, the touch display panel is in a touch mode for detecting a touch signal.
As mentioned above, the operation principle of the in-cell technology is a time-division multiplex control method for the touch mode and the display mode. That is, each frame time is divided into two time intervals which respectively transmit and process the display signal and touch signal. However, to reach an ideal touch effect, a higher report rate is required. In the conventional art, the time-division multiplex control method will limit the time period for processing the touch signal such that the report rate of the touch signal is limited.
In the conventional art, in order to overcome the above difficulties, generally, the frame rate is decreased to increase the time period for the touch signal. However, decreasing the frame rate means increasing the time interval. In the touch mode, although the switch T2 is turned off, a leakage current will still be generated in the circuit so as to decrease the voltage at two terminals of the liquid crystal capacitor and a normal voltage cannot be reached, which will seriously affect the display effect of the touch display panel.